The present invention relates to a fastener, and a structure for fastening a member to be fastened, for removably fastening a trim board, or the like, to a vehicle body panel.
A trim board of a vehicle is removably fastened to a vehicle body panel by using a fastener formed of a female member and a male member.
For example, in Patent Document 1, a pair of projections is provided along a circumferential direction on an outer edge side of a lower face of a head part of a male member. Also, recessed parts are provided along a circumferential direction on a shaft part of the male member, and are delineated by partition walls of the recessed parts.
Meanwhile, an engaging indented part in which the head part of the male member is to be fitted is provided on a flange of the female member, and saw tooth-shaped cams are formed on the upper face of the engaging indented part. Projections provided on the head part of the male member are made to be able to contact with inclined surfaces constituting the saw tooth-shaped cams.
Also, slits are provided along an axial direction on a cylindrical body part of the female member, and are made so that the partition walls of the male member can be inserted. The female member is inserted into insertion holes formed on the trim board and the vehicle body panel, and the shaft part of the male member is then inserted into the cylindrical body part of the female member, while aligning the positions of the partition walls of the male member with the positions of the slits of the female member.
Here, a plurality of split pieces is formed by the slits on the cylindrical body part, a claw part is placed projecting on an inner face of each split piece, and each claw part engages with a recessed part of the shaft part of the male member. The male member is thereby provisionally fastened on the female member in a state being incapable of rotation.
This state is a state in which the head part of the male member is raised up from the recessed part of the female member, while the projections of the male member are in contact with the inclined surfaces of the saw tooth-shaped cams. When the male member is rotated from this state, the projections of the male member ride past the top parts of the inclined surfaces of the saw tooth-shaped cams, and are guided to flat parts of the saw tooth-shaped cams, and the male member is pushed inward in a depth direction of the female member.
The claw parts of the split pieces are thereby locked on locking protuberances provided at an equal spacing along the circumferential direction of the shaft part of the male member, and each split piece expands outward, and the trim board and the vehicle body panel are sandwiched between the flange and the split pieces of the female member, so that the trim board can be fastened on the vehicle body panel.    Patent Document 1: Japanese Examined Utility Model Publication No. H6-45048
However, in the case when the shaft part of the male member is pushed from a side of the front end part of the shaft part, that is to say, in the case when the male member is pushed from the back, such as by tipping (a stone, or the like hits and the male member is pushed), during assembly, in a state in which the trim board is fastened to the vehicle body panel by means of this fastener, the projections of the male member being rotated along the inclined surfaces of the saw tooth-shaped cams of the female member. In other words, the claw parts of the split pieces engage with the recessed parts, the split pieces contract in diameter, and it becomes a state in which the male member and the female member can be removed from the trim board and the vehicle body panel.
An object of the present invention, in consideration of the above circumstances, is to provide a fastener, and a structure for fastening a member to be fastened, with which a sufficiently locked state can be maintained even when the male member is pushed from behind.